Conventionally, as methods for synthesizing a tetrahydropyran compound, a method of synthesizing a tetrahydropyran where 3,4-dihydro-2-butoxy-2H-pyran is catalytically hydrogenated by using a nickel catalyst is known (Journal of American Chemical Society Vol. 74, Page 2012 (1952)). However, this method has disadvantages in that the selectivity of tetrahydropyran compound is low in this method and that as a result, 5-butoxy pentanol is generated in a large amount.
Also, a method of synthesizing a tetrahydropyran compound through catalytic hydrogenation of 3,4-dihydro-2-alkoxy-2H-pyran compound or tetrahydro-2-alkoxy-2H-pyran compound by using tetrahydrofuran (THF) as a solvent and palladium activated carbon as a catalyst is disclosed (JP S62-093285 A). However, the reaction conditions for this method is reaction temperature of 150° C., reaction time of 20 hours and reaction pressure of 200 bar (approx. 20 MPa), which is too demanding to put into industrial application. Therefore, more milder reaction conditions are desirable.
Further, it is disclosed that tetrahydropyran (THP) is generated as byproduct in a method of synthesizing 1,5-pentanediol through hydrogenation of 3,4-dihydro-2-alkoxy-2H-pyran in the presence of water and a catalyst (JP 2001-64219 A). However, the method, which preferentially generates 1,5-pentanediol, is not preferred as a production process of a tetrahydropyran compound.
As examples of other methods of producing tetrahydropyran compounds, cyclization-dehydration reaction of a corresponding 1,5-pentanediol (JP H02-167274 A) and reduction reaction of a corresponding lactone (JP H01-290640 A) have been reported as available. However, these methods also involves problems of low yield of a tetrahydropyran compound and low selectivity and there is an increasing demand for a production method with a higher yield and a higher selection rate.